Recently, a zeolite shaped body composed of particles of a zeolite has been employed widely for catalysts, catalyst carriers, adsorbents and the like. Also, a zeolite layered composite comprising a porous ceramic, a metal, or the like and a zeolite membrane layered thereon has been employed for a molecular sieve membrane (a gas separation membrane, a pervaporation membrane). Along with the proceeding of such situation, there proposed are zeolite-layered composites using a variety of porous substrates and their production methods.
For example, proposed are methods using glass, mullite, a cordierite type ceramic, alumina, silica, and the like as a substrate for a zeolite membrane and methods using a metal or another substrate coated with an inorganic substance (Japanese Patent Laid-Open No. 59-213615).
Also, proposed (JP-A-60-28826) are composites each comprising a porous supporting body of a metal, an inorganic or polymer substance and a thin membrane of a cage type zeolite integrated in one surface. Among them, those having high affinity for a gel substance are proposed as especially preferable ones for the supporting body to be used and practically, it is proposed to use No. 7930 product produced by Corning Glass Works, generally called Vycorl glass, as an especially preferable one.
Further, a method proposed (JP-A-1-148771) relates to a method for crystallization of zeolite on the surface of a monolithic ceramic supporting body as a substrate which may have an oxide composition containing 4 to 45% by weight of silica, 8 to 45% by weight of alumina, and 7 to 20% by weight of magnesia; and practically proposed is a sintered monolithic supporting body of cordierite, glass, or a glass ceramic.
Further, another method proposed (Japanese Patent Laid-Open No. 6-32610) relates to a method for production of an A-type or faujasite type zeolite membrane using a substrate of a substance mainly containing silicon oxide. The method aims to solve the problem of inferior adhesion strength of a zeolite membrane to a substrate, where in a zeolite membrane is used as a substrate itself and the substrate surface is made to be a zeolite membrane owing to its constitution, thereby the synthesis and the adhesion can simultaneously be carried out to simplify the processes. To be practical, a substrate made of borosilicate glass, quartz glass, silica-alumina, mullite or the like is proposed.
Further, there is another proposal (JP-A-9-173799) which relates to a production method of a carrier zeolite membrane, and a membrane as the carrier, including an inorganic, organic, or mixed substance selected from the group consisting of a ceramic substance basically containing alumina, zirconia, or titanium oxide; a metal; carbon; silica; a zeolite; a clay; and a polymer.
Further, proposed is a zeolite porous body which is a porous ceramic substrate subjected to conversion treatment to a zeolite and has a large number of inner holes with prescribed sizes and a compressive fracture strength of 5 MPa or higher (JP-A-11-292651).
As described above, a variety of zeolite layered composites each comprising a substrate and a zeolite membrane layered or formed thereon have been proposed, however these composites have the following problems.
That is, as shown in FIG. 16, the thermal expansion coefficient of a zeolite shows a rather complicated behavior; at a temperature to around 200° C., it is extremely low but it becomes a negative coefficient value at a temperature higher than that. Hence, if a zeolite membrane is to be used at a temperature exceeding 200° C., the thermal expansion coefficient difference becomes extremely high between a substrate, for example, an alumina-based substrate and the membrane, resulting in cracking of the zeolite membrane owing to the thermal stress.
Further, depending on the types of zeolite membranes, at the time of synthesis, a casing agent or a crystallization promoting agent is required to be added. In the case of a zeolite membrane containing a template, the template is removed by calcining at about 500° C. and as shown in the thermal expansion curve of a MFI type zeolite in FIG. 17, the thermal expansion behavior (the thermal expansion curve before the calcining in FIG. 17) of a zeolite membrane containing a template significantly differs from the thermal expansion behavior (the thermal expansion curve after the calcining in FIG. 17) of a zeolite membrane containing no template, so that the thermal expansion difference becomes extremely wide between a substrate of such as an alumina substrate and the zeolite membrane and cracking takes place in the zeolite membrane owing to the thermal stress at the time of the calcining.
To such problems, said proposal examples cannot be sufficient counter measures to deal with the problems.
Further, the following are proposed as examples of those having double layer structures of a substrate and a zeolite membrane: asymmetric membranes (JP-A-7-505333) each comprising a macroporous layer formed practically only from a molecular sieve crystal with a prescribed thickness and an upper layer for molecular separation having a prescribed thickness and a prescribed effective diameter of fine pores and formed practically only from the molecular sieve crystal of the same type as that of the material of the macroporous layer; a structure (JP-K-11-511685) composed of three layers, a carrier, an intermediate layer, and an upper layer and in which the intermediate layer and the upper layer contain prescribed crystalline molecular sieves; and a zeolite composite membrane (International Laid-open No. WO 00/23378) produced by forming a zeolite membrane containing a template on a zeolite shaped body containing a template and then calcining to form the membrane and simultaneously remove the template. These membranes and structure are respectively excellent in the properties; the capability of precisely adjusting the size of the fine pores and the capability of effectively preventing occurrence of cracking.
However, regarding the zeolite shaped body obtained as the zeolite composite membrane (International Laid-open No. WO 00/23378) formed simultaneously with removal of the template from said substrate, since the raw materials (a dried gel) are obtained by stirring and kneading preparation solutions of silica sol and tetrapropylammonium hydroxide (TPAOH), the obtained dried gel is easy to contain particles with different particle diameter and heterogenously dried state, so that dense and sparse parts and degranulated parts are easily formed in the zeolite particle portions in the microstructure after the crystallization treatment and therefore it is not necessarily satisfactory one.
Further, regarding a method including processes of previously dispersing a template such as tetrapropylammonium (TPA) in a dried gel and then converting it to a zeolite by treatment with steam, since it has conventionally been thought necessary to stir a mixture solution of a gel and a template until they are dried as a dried gel production process, the following processes have generally been employed; heating mixture solution of the gel and the template to about 80° C. to evaporate water and successively continuously stirring (kneading) the solution until the mixture is sufficiently dried [N. Jappar, Q. Xia, and T. Tatsumi, J. Catal. 180, 132-141 (1998); R. Bandyopadhyay et al., Micropor. Mater. 32(1999) 81-91; Masahiko Matsukata, P. R. H. Prasad Rao, Korekazu Ueyama, Proceedings of the 11th Zeolite Research Meeting, Japan Association of Zeolite, in Matsuyama, 1995, A22; P. R. H. Prasad Rao, Proceedings of the 12th Zeolite Research Meeting, Japan Association of Zeolite, at Sophia University, 1996, A18.; P. R. Hari Prasad Rao & M. Matukata, Chem. Commun. (1996), p1441-1442, P. R. Hari Prasad Rao, K. Ueyama, M. Matsukata, Appl. Catal. A: General 166 (1998) 97-103; and the like].
However, such a method comprising the dried gel production process comprises complicated production process and is thus not suitable for mass production and further, the obtained dried gel is, as same as the case of said International Laid-open No. WO 00/23378, easy to be heterogenous in the size of the particle diameter and not homogeneous in the dried state and for that, in the micro-structure after the crystallization treatment, dense and sparse parts and degranulated parts are easily formed among the zeolite particle portions and the method is not necessarily satisfactory.
Further, in the case where the membranes or the structure (zeolite layered composites) are used as gas separation membranes of molecular sieve membranes and pervaporation membranes, it is required to improve the use efficiency by decreasing the pressure loss at the time of passing a gas or a liquid through the membranes and the substrate. If the dense parts of particles of the substrate, which are causes of increase of the pressure loss, are reduced or the particle size of the substrate is enlarged in order to reduce the pressure loss, the mechanical strength as a substrate for supporting a zeolite membrane is decreased (the reduction in the pressure loss in the substrate and the improvement of the mechanical strength are in an antinomic relation), so that it is extremely difficult to obtain those capable of satisfying both of the reduction in the pressure loss and the improvement of the mechanical strength and any membrane or structure capable of satisfying such properties has not been obtained so far.
The present invention is developed in consideration of said problems and aims to provide a zeolite shaped body by forming a zeolite membrane thereon without causing cracking, and capable of satisfactorily reducing pressure loss and improving mechanical strength when it is used as a gas separation membrane of a molecular sieve membrane, and a pervaporation membrane and the like; a zeolite layered intermediate body comprising the zeolite shaped body and a zeolite membrane containing a template and layered thereon; a zeolite layered composite formed by calcining the zeolite layered intermediate body, and their efficient production methods.